The present invention is directed, in general, to power amplifier circuits in a base station and, more specifically, to a system for improving the efficiency of signal power amplification in a base station.
Power amplifiers in a code division multiple access (CDMA) wireless communication system increase the strength of an input signal without appreciably altering other signal characteristics of the input signals. Because CDMA signals are a non-constant envelope, the signal peak to average ratio can be very large, on the order of 12 dB or more. This possibility for large peak power requires the power amplifiers to operate with a large amount of xe2x80x9cbackoffxe2x80x9d from the optimum P1 dB point to maintain linear operation during peak power periods.
Power amplifiers with large backoffs exhibit extremely poor efficiency. Greatest efficiency is achieved at higher power levels nearest the gain compression point. Efficiency decreases proportionally to the square root of Pout as Pout is reduced from the 1 dB compression point (P1 dB) for class AB amplifiers.
FIG. 6 depicts graph 600 of the probability of observing a certain peak to average ratio in a CDMA base station transmit signal. For example, based on curve D, an amplifier designed for a CDMA output power of 10 W (40 dBm) would need to have a peak power capability of approximately 125 W (51 dBm) to accommodate the large peaks that occur in the input signal. The probability of occurrence of signal peaks 602 being greater than 11 dB above the average power is less than 0.1%.
Power amplifiers with large backoffs exhibit extremely poor efficiency. A power amplifier""s greatest efficiency is achieved at higher power levels nearest P1 db, the gain compression point. Efficiency decreases proportional to the square root of Pout in class AB operation with reduced power levels (increased backoff) and increased power consumption.
There is therefore a need in the art for an improved base station power amplifier capable of handling short term power increases. In particular, there is a need in the art for a power amplifier with improved power amplification efficiency and decreased power consumption.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide, for use in a base station power amplifier, a first and second amplifier stage for amplifying a received RF signal. A controller is provided that samples the incoming signal to determine its power level. If the signal power level is below a predetermined threshold, the controller directs the signal to the first amplifier stage which provides low power amplification. If the signal is above the threshold, the controller passes the signal to the second amplifier stage which provides high power amplification.
In an advantageous embodiment of the present invention a first set of pin-diode switches in conjunction with quarter-wavelength lines is provided for opening and closing a radio frequency input for the first amplifier.
According to one embodiment of the present invention, a second set of pin-diode switches in conjunction with quarter-wavelength lines is used for opening and closing the radio frequency input for said second amplifier.
According to another embodiment of the present invention, a detection circuit is utilized for sampling an incoming radio frequency signal to determine a power level of the signal and a time delay circuit delays the signal so that the controller is able to make switching decisions.
According to still another embodiment of the present invention, a switch is provided for switching the RF signal to either the first amplifier or the second amplifier depending on the power level of the incoming signal. If the power level is below a predetermined threshold, the signal is passed through the main, first, amplifier stage. If the power level is above the threshold, the signal is passed through the second amplifier stage.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.